1. Field of the Invention
The present invention relates to a steering wheel for allowing the driver to control the direction of vehicle travel, and more particularly to a steering wheel having a construction in which decorative portions are partially provided on a ring portion in a longitudinally circumferential direction thereof.
The present application is based on Japanese Patent Application No. 2000-188733, which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, there is disclosed in Unexamined Japanese Patent Publication No. Hei. 11-91588 a steering wheel which is representative of steering wheels having a construction in which decorative portions are provided on a ring portion of the steering wheel to extend in a longitudinally circumferential direction thereof for providing a feeling of wood. In this steering wheel, a core bar covering portion made of a soft synthetic resin to cover a core bar of a substantially annular ring portion gripped for steering is provided along the circumference of the core bar of the ring portion, and decorative portions are partially disposed on the core bar covering portion to extend in a longitudinally circumferential direction of the ring portion. The decorative portions are made of a hard material and are each formed by combining together an upper decorative portion having a substantially inverted U-shaped cross section and a lower decorative portion having a substantially U-shaped cross section.
In a conventional steering wheel of this type, when an impact force is applied to a central portion on the front side of the decorative portion on the ring portion from above due to collision of an automobile vehicle, the core bar is bent and plastically deformed into substantially a V shape as viewed from a side of the ring portion, with a front side of the ring portion being bent downwards from the plane of the ring portion which extends along an upper surface of the ring portion.
In the conventional steering wheel of this kind, however, since the core bar of the ring portion is bent downwards and deformed into substantially the V shape as viewed from the side of the ring portion, there has been a case where the upper decorative portion is lifted from the lower decorative portion.
Note that backward and forward directions of the steering wheel of the invention when installed on an automotive vehicle correspond to backward and forward directions of the automotive vehicle when the vehicle advances linearly, and that upward and downward directions of the steering wheel correspond to upward and downward directions along axial directions of the steering shaft.
In addition, since the core bar at the decorative portion is bent and deformed in such a manner as to project downwards when the impact force is applied as described above, a tensile force is applied to the lower decorative portion, while a compressive force is applied to the upper decorative portion. Then, since the upper and lower decorative portions are combined together, in addition to the compressive force, a reaction to the tensile force applied to the lower decorative portion is synergistically applied as a compressive force to the upper decorative portion from a longitudinally or transversely circumferential direction of the ring portion. Due to this, distortion generated in the upper decorative portion by the compressive forces grows to thereby produce breaks or cracks thereat.
The invention was made in view of these situations, and an object thereof is to provide a steering wheel which can suppress lifting of end portions of an upper decorative portion from a lower decorative portion, as well as the production of breaks or cracks in the upper decorative portion which are both generated when an impact force is applied to the decorative portion of a ring portion.
According to a first aspect of the invention, there is provided a steering wheel comprising a substantially annular ring portion gripped for steering which is constituted by a core bar and decorative portions which cover an external surface of the core bar, wherein the decorative portions are disposed partially on the core bar to extend along a longitudinally circumferential direction of the ring portion, while the decorative portions are disposed to cover the external surface of the core bar along the full circumference thereof in a transversely circumferential direction of the ring portion when an upper decorative portion having a substantially inverted U-shaped cross section and a lower decorative portion having a substantially U-shaped cross section which constitute each of said decorative portions are combined together, the steering wheel being characterized in that reinforcement ribs are formed on the core bar at positions in the vicinity of end portions of one of the decorative portions in such a manner that bend deforming portions of the core bar which allow the ring portion to be inclined partially from the plane of the ring portion when an impact force is applied to the one of the decorative portions on the ring portion are dislocated from a location where the decorative portion is disposed.
According to a second aspect of the invention, there is provided a steering wheel comprising a substantially annular ring portion gripped for steering which is constituted by a core bar and decorative portions which cover an external surface of the core bar, wherein the decorative portions are disposed partially on the core bar to extend along a longitudinally circumferential direction of the ring portion, while the decorative portions are disposed to cover the external surface of the core bar along the full circumference thereof in a transversely circumferential direction of the ring portion when an upper decorative portion having a substantially inverted U-shaped cross section and a lower decorative portion having a substantially U-shaped cross section which constitute each of the decorative portions are combined together, the steering wheel being characterized in that a stress concentration portion is formed in an inner circumferential surface of the lower decorative portion at at least a position in the vicinity of a central portion of the lower decorative portion in the longitudinally circumferential direction of the ring portion.
In the steering wheel according to the first aspect of the invention, since the reinforcement ribs are formed on the core bar at the positions in the vicinity of the end portions of one of the decorative portions in such a manner that the bend deforming portions of the core bar which allow the ring portion to be inclined partially from the plane of the ring portion when an impact force is applied to the one of the decorative portions on the ring portion are dislocated from the location where the decorative portion is disposed, even if the impact force is applied to a position in the vicinity of a central portion on the front side of the decorative portion on the ring portion, the decorative portion is bent and deformed not at the locations in the vicinity of the end portions of the decorative portion but at the locations dislocated from the location where the decorative portion is disposed, whereby the lifting of the upper decorative portion from the lower decorative portion is suppressed.
Consequently, with the steering wheel according to the first aspect of the invention, the lifting of the upper decorative portion from the lower decorative portion can be suppressed which would otherwise occur when an impact force is applied to the decorative portion on the ring portion.
In the steering wheel according to the second aspect of the invention, the stress concentration portion is formed in the inner circumferential surface of the lower decorative portion at least the position in the vicinity of the central portion of the lower decorative portion in the longitudinally circumferential direction of the ring portion. Due to this, when an impact force is applied to the position in the vicinity of the central portion on the front side of the ring portion, the core bar is bent and deformed in such a manner as to project downwards, and a tensile force is applied to the lower decorative portion to thereby brake the stress concentration portion. This prevents a reaction to the tensile force on the lower decorative portion from being applied to the upper decorative portion as a compressive force, whereby no force but the compressive force which is originally applied to the upper decorative portion is permitted to be applied to the upper decorative portion, the occurrence of deformation in the upper decorative portion being thus reduced. As a result of this, the generation of breaks or cracks in the upper decorative portion can be suppressed.
Consequently, with the steering wheel according to the second aspect of the invention, the generation of breaks or cracks in the upper decorative portion can be suppressed which would otherwise occur when an impact force is applied to the decorative portion on the ring portion.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.